1. Field of the Invention
The present invention relates to a laser diode driver, and more particularly to a high power, high pulse repetition frequency (PRF), pulsed laser diode driver.
2. Description of the Prior Art
Generally, semiconductor laser drivers have a very high circuit impedance. Due to severe impedance mismatch between a laser driver having a high impedance and a semiconductor laser having an extremely low impedance, rather than the electrical energy is used to operate the semiconductor laser, most of it is lost in the form of heat.
For the operation of the high power semiconductor laser driver, current beyond threshold level should be supplied to the semiconductor laser driver. The lost energy has to be compensated.
Therefore, such a conventional high power, pulsed laser driver is designed with much high power capability, taking into consideration energy to be lost as well as energy required to operate the laser.
In the conventional high power, pulsed driver, as the lost energy is increased, the power capability goes up steeply. As a result, the capabilities of the laser driver such as the rise and fall times, pulsewidth and PRF of the output laser pulse deteriorates rapidly, while steeply increasing the size and weight of the driver.
For solving such problems encountered in the conventional laser driver, there has been proposed a high power, PRF, pulsed laser diode driver. This laser diode driver is disclosed in Korean Patent Application No. 94-2144 filed by the applicant.
This laser diode driver utilizes a non-uniform, low impedance stripline structure as its energy storage capacitor to obtain a highly efficient laser diode driver circuit. Further, in a matched impedance condition, two-way wave transit time of the non-uniform impedance stripline structure becomes the pulsewidth of the high power laser output pulses. Therefore, by properly designing the energy storage capacitor, laser output pulses having a pulsewidth with only a few nanoseconds are obtained.
However, due to practical reasons such as eye safety, effective distance, precision and high speed data communications, it is highly desirable to produce high peak power laser pulses with the pulsewidth much less than a few nanoseconds. For the generation of the high peak power, laser pulses with a few nanoseconds pulsewidth, utilization of the non-uniform impedance stripline structure as the energy storage capacitor is very effective way.
In an ideal operating condition, the shortest output laser pulse width, obtained from a non-uniform stripline structure, is about equal to the two-way wave transit time in this energy storage capacitor. Therefore, as the length of the non-uniform impedance stripline becomes short, accordingly, the pulsewidth of the laser output pulses becomes narrow. Hence, the output light pulses with a few nanoseconds pulsewidth is obtained by simply reducing the physical length of the energy storage capacitor until the two-way wave transit time of this capacitor becomes a few nanosecond.
But for the generation of the output laser pulses with pulsewidth less than a few nanoseconds, the thing is not that simple. Merely miniaturizing the physical length of the energy storage capacitor will not produce an ultra-narrow pulsewidth. There is limit. Too excessively miniaturized stripline which is required condition for the ultra-narrow pulsewidth (pulsewidth less than a few nanoseconds) could result in too small capacitance to store necessary electrostatic energy in the energy storage capacitor. Further,stray inductance will adversely affect the properties of the output pulses. Therefore, a new technique has to be devised.